In order to configure a modlog channel, you will need to get the channel ID of the channel you wish to use.
You can get this ID by enabling Developer Mode in your user settings (Instructions)
Once you have enabled Developer Mode, Right Click on the channel you wish to copy the ID for.
Once you have copied the ID, insert it into the command.
s!add-modlog <id> sp!add-modlog <id>
Do not include the <> when using the command.
If you wish to remove a modlog channel. Follow the same steps to get the channel ID and insert it into the following command.
s!remove-modlog <id> sp!remove-modlog <id>